I want to make the head and arms as different objects which are as single mesh now with the bone structure intact
I'm not entirely sure if it does or doesn't corrupt your animation data as the weights possibly change but here a workflow worth a try:

Select the mesh and go in edit mode 'tab'.
Select the head press Y to split the geometry.
Repeat the process for the arms.
While still being in edit mode press P and select &quot;separate by loose parts&quot;.

This should separate the geometry into parts. I'm not sure how this will affect the armature / binding and animations.
-&gt; run an animation to check if that already solved your issues
If the bindings are lost (arms / head etc, don't react to the bones):

Select all objects you want to bind to the rig.
Select the rig last.
Press Ctrl+P and select &quot;With Automatic Weight&quot;.

Run an animation - if the deformations are weird, you probably have to take a look into weight painting.